We label the external edges of the five-point ziggurat graph shown in Fig REF (b) with \(Z_1\)  on the lower right corner, increasing in clockwise order, and we label the lower (upper) loop with \(\mathcal {L}_1\)  (\(\mathcal {L}_2\) ) respectively. It is well-known that the seven on-shell conditions (i.e., the double box heptacut) admit six distinct one-parameter families of solutions (see for example [1]} for a nice discussion):
2
L1 = (Z1, Z2 + (1-) Z3)  L1 = (Z1, Z2 + (1-) Z3)
